1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic copying machine, a laser printer, or the like, for forming an image by an electrophotographic process.
2. Description of the Related Art
In recent years, image forming apparatuses of this type has been reduced in size. With this reduction in size, in order to improve the assembly and maintenance performance, constituent parts housed in the apparatus main body are often formed into a unit.
For example, an image carrier, a charger, a developing device, and a cleaning device are formed as an image forming process cartridge. In addition, exposure/optical systems for exposing the image carrier surface to form an electrostatic latent image on the image carrier prior to a developing operation are formed as an optical unit.
In a conventional apparatus, the image forming process cartridge, the optical unit, a transfer unit for transferring a developing agent image, which is formed on the image carrier, onto a transfer medium, and the like are mounted in the main body while they are positioned at predetermined positions by positioning pins, studs, independent positioning frames, guides, and the like, respectively arranged on the apparatus frame.
If, however, the process cartridge, the optical unit, the transfer unit, and the like are positioned by the positioning pins, the studs, the positioning frames, the guides, or the like, it is difficult to position these members precisely. The relative positions between these members greatly influence image quality. Furthermore, problems are posed in terms of assembly performance and manufacturing cost.